ScalaInterceptors - notbrain/Play20 GitHub Wiki

Intercepting requests

Using Filters

The filter component allows you to intercept requests coming to the application, transform request and responses. Filters provide a nice ability to implement cross-cutting concerns of your application. You can create a filter by extending the Filter trait and then add the filter to Global object. The following example creates an access log filter that logs the result of all the actions:

import play.api.mvc._

object Global extends WithFilters(AccessLog)

object AccessLog extends Filter {
  override def apply(next: RequestHeader => Result)(request: RequestHeader): Result = {
    val result = next(request)
    play.Logger.info(request + "\n\t => " + result)
    result
  }
}

The Global object extends the WithFilters class that allows you to pass one more filters to form a filter chain.

Note WithFilters now extends the GlobalSettings trait

Here is another example where filter is very useful, check authorization before invoking certain actions:

object Global extends WithFilters(AuthorizedFilter("editProfile", "buy", "sell")) with GlobalSettings {}
 
object AuthorizedFilter {
  def apply(actionNames: String*) = new AuthorizedFilter(actionNames)
}
 
class AuthorizedFilter(actionNames: Seq[String]) extends Filter {
  override def apply(next: RequestHeader => Result)(request: RequestHeader): Result = {
    if(authorizationRequired(request)) { 
      /* do the auth stuff here */ 
      println("auth required")
      next(request) 
    }
    else next(request)
  }
 
  private def authorizationRequired(request: RequestHeader) = {
    val actionInvoked: String = request.tags.getOrElse(play.api.Routes.ROUTE_ACTION_METHOD, "") 
    actionNames.contains(actionInvoked)
  }
}

Tip RequestHeader.tags provides lots of useful information about the route used to invoke the action.

Overriding onRouteRequest

One another important aspect of the Global object is that it provides a way to intercept requests and execute business logic before a request is dispatched to an Action.

Tip This hook can be also used for hijacking requests, allowing developers to plug-in their own request routing mechanism.

Let’s see how this works in practice:

import play.api._
import play.api.mvc._

// Note: this is in the default package.
object Global extends GlobalSettings {

  override def onRouteRequest(request: RequestHeader): Option[Handler] = {
     println("executed before every request:" + request.toString)
     super.onRouteRequest(request)
  }

}

It’s also possible to intercept a specific Action method, using Action composition.

Next: Testing your application

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